Source: light fixtures Author: Beijing Jiaotong University Dong Xinyu Wang Zhanguo Li Xingchun
Abstract: The use of Beijing Xing Wei Limu Company at-rfmod06 series of radio base station modules with pic16 microcontroller-based development for 125 khz frequency of at88rf256 RF card reader. Focuses on the hardware module to connect the base station and base station on the radio how to read and write control card, and the corresponding applications.
Keywords: RF card reader; at88rf256; pic microcontroller; design
With the computer and embedded system development, ic card has been integrated into people’s daily lives and develop into several categories, including, non-contact ic card caused the emergence of particular concern. Are non-contact RF card ic card, ic card, it avoids the common and the physical contact between the reader, reducing the wear of the card, it has been widely welcomed. RF is radio frequency identification cards (rfid) component of the system.
RFID (radio frequency identification, to f referred rfid) technology is the rise of the 1990s, an automatic identification technology. It uses radio frequency non-contact way of two-way communication and exchange of data, in order to achieve identification purposes. A typical system consists of rfid tags (tag), reader (read / write device) and data exchange and management system, etc. Tag, also known as radio frequency card, with the intelligent reader and encrypted communications.
2 system working principle and hardware design
I designed the RF system consists of a computer card reader, card reader and RF components, system architecture shown in Figure 1.
2.1 RF Card Reader
RF card reader mainly by picl6 type microcontroller and Beijing Weili Mu Xing produced at-rfmodcl6 series of radio base station modules. The module uses a common u2270b type non-contact card reader base station circuit. By the integrated circuit chip power supply, oscillator and coil actuator composed of energy transmission lines, used to power radio cards work; also incorporates signal amplification and antenna driver circuit to complete the card with the radio signal between the sending and receiving . at-rfmod06 with picl6 interface circuit shown in Figure 2.
af-rfmod06 module pin functions as shown in Table 1. The module uses a separate 9-pin package, the internal integration of the clock, RF, filtering, amplification, modulation and demodulation and other analog circuits, in accordance with Figure 2 digital interface circuits connected, simply select the appropriate antenna and the resonant capacitor can be complete RF circuit design.
In Figure 2, the base station antenna and the oscillator capacitor formed lc oscillator circuit, the oscillation frequency of the system requirements have limited 125 khz (± 5%), the antenna can reach a maximum oscillation amplitude 120 v, generally not greater than 80 v, can and antenna coil through a resistor in series to adjust the antenna’s oscillation amplitude. Oscillation capacitor voltage value should be greater than 100 v. After repeated testing, parameter is set to c = 2 200 df, l = 680μ h. r = 82ω.
2.2 at88rf256 RF card
at88rf256-12 atmel card is U.S. based company introduced a 125 khz frequency proximity cards can be encrypted. The amount of data is 256 bits. As a typical low-frequency, encryption, and can read and write cards. at88rf256 a 12 on the market have a wide range of applications. at88rf256-12 from the circuit and coils. Internal structure of the circuit shown in Figure 3.
L1 and l2 circuit pin connector pin and the coil, the coil inductance of 10.1 mh, the card operates at 125 khz. Its work by the on-chip power circuit built-in capacitance of the coil and lc oscillator power storage available. at88rf 256-12 design of the capacitor built into the circuit, reducing the card processing chain. But also improves the module into the card and the yield and reliability. lc oscillations generated by the card’s power supply circuit transformed respectively to control part and eeprom unit.
3 codec and software process
3.1 RF card and command register
The eeprom is divided into lo-card page. Including 32 per page, its contents are shown in Table 2